1. Field of the Invention
The present invention relates to a magnetoresistive film which is applied to a magnetoresistive element (MR element) such as a magnetoresistive magnetic head (MR head) or a magnetic sensor (MR sensor) for reading an information signal from a magnetic medium.
2. Description of the Background Art
A magnetoresistive element, which is adapted to detect a change in electrical resistance of a magnetic substance caused by application of a magnetic field for measuring the magnetic field strength or its change, must have a high magnetoresistance ratio and excellent magnetic field sensitivity, i.e., a small operating magnetic field, in general.
There has recently been proposed a magnetoresistive element employing a magnetoresistive film of a sandwich film structure having first and second ferromagnetic layers which are partitioned or separated from one another by a layer of a non-magnetic metal, as a magnetoresistive element having a high magnetoresistance ratio and high magnetic field sensitivity. Such a magnetoresistive element utilizes a spin valve effect of implementing parallel and antiparallel states of magnetization through deviation in magnetization transition between the ferromagnetic layers. For example, Japanese Patent Laying-Open No. 4-358310 (1992) discloses a magnetoresistive element having a sandwich film structure consisting of first and second ferromagnetic layers which are partitioned by a layer of a non-magnetic metal body so that these ferromagnetic layers are different in coercive force from each other.
Such a magnetoresistive element utilizes the aforementioned spin valve effect to implement parallel and antiparallel states of magnetization between the ferromagnetic layers resulting from difference in coercive force, thereby causing a magnetoresistance change. In the magnetoresistive element utilizing such a spin valve effect, it is necessary to eliminate a magnetic coupling force between the ferromagnetic layers which are positioned on both sides of the film of the non-magnetic metal body to the utmost. In other words, a high magnetoresistance change (high MR ratio) and high magnetic field sensitivity (low Hs) can be attained when the magnetic properties of the first and second ferromagnetic layers are independently changed with no mutual interference.
In order to reduce magnetic interaction between the first and second ferromagnetic layers, it is necessary to sufficiently increase the thickness of the non-magnetic metal film which is interposed therebetween. When the thickness of the non-magnetic metal film is increased, however, the proportion of by conduction electrons subjected to spin-dependent scattering, which are regarded as being mainly generated in the interface between the ferromagnetic layers, among all conduction electrons in the non-magnetic metal film is reduced. Therefore, an influence which is exerted on the conduction electrons of the non-magnetic metal film by magnetization changes of the first and second ferromagnetic layers is so reduced that a high magnetoresistance change cannot be attained.
When the thickness of the non-magnetic metal layer is reduced, on the other hand, ferromagnetic (ferric) magnetic coupling is caused between the first and second ferromagnetic layers to reduce the independence of magnetization transition of the first and second ferromagnetic layers. Thus, a high magnetoresistance change cannot be attained.